(1) Field of the Invention
The present invention relates to a method of piloting a rotary wing aircraft having a tail rotor suitable for swiveling about a swivel axis, and the invention also relates to such an aircraft.
More particularly, the invention relates to aircraft provided firstly with a rotary wing for providing at least some of the lift of the aircraft, and secondly with a tail rotor suitable for opposing the torque generated by the rotary wing on the airframe of the aircraft, the tail rotor being capable of swiveling about an axis in order to contribute to propelling the aircraft.
(2) Description of Related Art
The performance of a helicopter is conventionally limited by the speed of rotation of the main rotor that constitutes the rotary wing. The speed of the blades of said main rotor relative to the surrounding air must in particular remain locally less than the speed of sound. At high speed, the lifetime of the component is reduced in particular because of the appearance of vibration.
Consequently, in order to obtain a rotary wing aircraft that is capable of moving at high speed, e.g. for ecological reasons, it is possible to use an additional source of propulsion in order to reduce or eliminate the cyclic pitch of the blades of the main rotor so as to make it possible to reduce the speed of rotation of said main rotor at high forward speed.
Document FR 1 511 006 suggests using a tail pusher propeller associated with the conventional anti-torque tail rotor of a helicopter. The pusher propeller then serves to off-load the main rotor of at least a fraction of its propulsion function.
In order to optimize the performance of a helicopter, document FR 1 017 976 suggests using an aircraft fitted with a rotary wing and a tail rotor suitable for swiveling about a swivel axis.
In a first mode of operation, the tail rotor is used to counter the torque generated by the rotary wing and to provide yaw control.
In a second mode of operation, the tail rotor swivels so as to contribute to propelling the aircraft, with yaw control being obtained by steering the tail rotor on either side of a neutral position.
Such an aircraft is sometimes referred to as a “vector-thrust helicopter”.
Document U.S. Pat. No. 3,155,341 presents a convertiplane having a main rotor, a swiveling tail rotor, and a wing, the convertiplane being suitable for changing over from a helicopter mode to an airplane mode.
Document FR 1 536 412 presents a mechanism for controlling the swiveling of a tail rotor of a convertiplane. That mechanism has a single outlet for controlling pitch and two inlets for controlling yaw in helicopter mode and controlling thrust in airplane mode, with the transition from one kind of control to the other taking place progressively. Thus, in airplane mode yaw control becomes inoperative whereas in helicopter mode thrust control is inoperative.